Fix errors in Sky detected by Dart analyzer

sky/framework/components/radio.dart

Index: sky/framework/components/radio.dart
diff --git a/sky/framework/components/radio.dart b/sky/framework/components/radio.dart
index 4f45aa36d3acf3d503c26b1ec0e19b256571dc6e..edc79374665f4290bf2eae4debaf9bad50fc6ba7 100644
--- a/sky/framework/components/radio.dart
+++ b/sky/framework/components/radio.dart
@@ -57,8 +57,8 @@ class Radio extends ButtonBase {
   Node build() {
     return new Material(
       styles: [highlight ? _highlightStyle : _style],
-      children: value == groupValue ? [new Container( style : _dotStyle )] : []
-    )
+      children: value == groupValue ? [new Container(styles: [_dotStyle] )] : []
+    );
   }
 
   void _handleClick(_) {